Electric power control modules supply power to step motors in response to input signals received by the modules. Each module may supply a number of different types of power. Conventionally, each module is connected to a power source by heavy-duty power cables. Two cables are required for each type of power supplied to a module. Each module includes a header connector which mates with a plug connector mounted on the ends of each pair of power cables supplying a type of electric power to the module. A number of power control modules are positioned together to facilitate connecting the modules to the power source and inspection and servicing of the modules.
However, connecting each module to the power source using pairs of heavy-duty cables for each required type of electric power is difficult, expensive and inconvenient. Sets of different length power cables must be cut, terminated and connected to the modules and to the power source. The large number of cables must be properly routed between the power source and the control modules. This is a time-consuming and expensive process. Servicing the cables and modules can be difficult.
Contact members on adjacent modules are connected by high voltage, high amperage bridge assemblies using one-piece copper conductors. These bridge assemblies have long conductor strips with copper U-bends at the strip ends. The U-bends hold the copper strips on the contact members.
High amperage current flowed through conventional bridge assemblies can heat and weaken the copper U-bends sufficiently to reduce contact pressure between the conductor strips and the contact members. This can reduce current flow between modules.
Accordingly, there is a need for an improved modular power distribution system which efficiently connects a power source to a number of control modules without having to connect a pair of cables from the source to each module for each type of power supplied to the module. The improved system should include pairs of modular power conductors extending between modules. The pairs of conductors for each type of power should be connected to the power source by power cables extending to a first or end module only and should be connected to additional modules by pairs of series-oriented conductors having modular distribution units and bridge assemblies connecting adjacent distribution units. The distribution units should be removably mounted on the control modules, and the bridge assemblies should be easily and removably mounted on the distribution units to facilitate installation and servicing.
There is also a need for an improved bridge assembly with copper conductors and heat-resistant springs which hold the copper conductors against contact elements on the modules so that current heating of the conductors does not impair the springs and does not reduce current flow.